The present invention relates to a valve actuating apparatus for an engine.
Japanese Patent Application First (unexamined) Publication Nos. 63-57806 and 63-167016 disclose a valve actuating apparatus. The known valve actuating apparatus comprises a mechanism to releasably interconnect the adjacent two rocker arms which are engaged with a low speed cam lobe and a high speed cam lobe integral with a camshaft, respectively. The rocker arms are formed with mating bores receiving a plunger. The plunger is moveable between a first position in which the plunger is disposed in one of the mating bores and a second position in which the plunger is inserted into the other plunger and thus disposed in both of the mating bores. When the plunger is in the first position, the two rocker arms move separately, while when the plunger is in the second position, they move as a unit.
Owing to the use of the plunger and mating bores, this mechanism requires a high degree of accuracy in machining the mating bores and the plunger.
There has been proposed a valve actuating apparatus which does not use a plunger nor bores which demand high degree of accuracy to machine.
The copending U.S. patent application Ser. No. 07/873,362 and German Patent Application No. P 42 13 865.5 disclose a valve actuating apparatus of this kind. This apparatus comprises a rocker arm supported by a rocker shaft for contacting with a first or low speed cam lobe and a valve stem, a lost motion mechanism, a free cam follower and a prop. The lost motion mechanism includes a stationary portion defining a pedestal fixed to the rocker arm and a moveable portion received by the stationary portion. The free cam follower includes a cam face adapted for contacting with a second or high speed cam lobe. The prop is supported by the free cam follower for movement between a first position in which the prop supports the free cam follower on the moveable portion of the lost motion mechanism and a second position in which the prop supports the free cam follower on the pedestal of the lost motion mechanism.
For reliable operation of this valve actuating apparatus, it is required to hold the cam face of the free cam follower in a predetermined relationship with the second cam lobe, and it is also required that the free cam follower supports the prop rigidly against torque applied to the prop, but loosely enough to allow quick and smooth movement of the prop between the first position thereof and the second position thereof.
Thus, there is still a demand on high accuracy in machining parts in order to keep the product-by-product variability sufficiently low, making a reduction in manufacturing cost difficult.
An object of the present invention is to improve the previously proposed valve actuating apparatus of the kind which is disclosed in U.S. patent application Ser. No. 07/873,362 and German Patent Application No. P 42 13 865.5 such that the degree of accuracy in machining parts may be lowered with the product-by-product variability kept sufficiently low and thus a reduction in manufacturing cost results.